1. Field of the Invention
This invention relates generally to obscuration smoke detectors and more particularly is directed towards a new and improved obscuration smoke detector and method for the operation thereof in which automatic self-calibration functions are performed on a regular basis.
2. Description of the Prior Art
When smoke detectors are tested, one of the techniques used to determine the sensitivity of the unit is to place a photodetector at a distance from the light source, i.e. 5 ft. in the case of Underwriters Laboratory. The sensitivity of the detector is then measured in terms of obscuration per foot with typical values ranging from 0.2% to 4% per foot. Although such a device has good short term stability, it has poor long term stability and requires calibration prior to each test. Further, it is affected by temperature changes, and by dirt or film build-up on the optical surfaces of the components which cause transmission changes greater than would be caused by smoke alone.
Accordingly, it is an object of the present invention to provide improvements in smoke detectors and the method of operation thereof. Another object of this invention is to provide a thermally stable, self-calibrating, obscuration smoke detector and method of operating said detector.